Hi,
I should have isoraise here?
However I don't have much info on CO, and MP's stack was a bit small, so was a bit unsure how to proceed here, I ended up calling to keep MP in, maybe get some free cards, but think I have to fold to CO cbet?
I could call to reevaluate turnm but nothing much will be gained by it, if CO is a reg he will not barrel unless he is absolutely sure he is ahead in a multiway.

As to whether you should re-raise it depends on the CO's Ft3bet stat. If he is calling wide it might be ok. Vs unknown I'd assume the best option is to flat.

On the flop when CO bets into 3 opponents (one of which is a shortstack), folding is probably the best option. To an extent you are being squeezed here because you never know if MP might check/shove all-in.